Conventional turbines generally extract energy from a fluid flow, such as air or water, by decreasing the speed of flow. Turbines come in varying sizes and configurations depending on the application. Some turbines are designed for small, specific applications. For example, simple wind turbine installations are used in remote locations to provide power to small communities. Independent power producers and utilities often use several larger wind turbines on a parcel of land or offshore site to generate power transmitted to a power grid. Turbines have also been used in water-based applications such as in the current flow of rivers.
Turbines and power generation projects are often subject to unique environmental and economic pressures. The size and scale of wind turbine projects in particular present several issues. Cost factors are the forefront of many turbine projects because of the delicate balance of high upfront capital costs to long-term revenues. Cost concerns involve ongoing maintenance and operation costs as well as build-out costs. The complexity and scale of wind turbines also leads to significant costs associated with transportation, capital, and labor. Large wind turbine projects also generally create additional concerns such as noise disturbances and visual impact at site locations.
In response to these concerns, there has been an increasing effort to improve performance and reduce the overall cost and environmental impact of turbines and turbine systems. Such efforts thus far have focused on cost of delivered energy, performance, material usage, system longevity and reliability, turbine blade performance and noise among other factors.
At a basic level, however, conventional turbines generally operate based on similar principles. A typical turbine includes several members, for example, blades, for engaging the fluid flow. The blades are positioned in the fluid flow and connected at a hub. The hub connects to a shaft and drivetrain assembly which then drives a generator.
Recently there has been an increased effort to improve turbine performance and address various environmental and economic issues. One focus has been to reduce the costs associated with turbines by reducing material usage, increasing performance, and increasing the operational life of the turbine. There is a constant need to reduce costs and increase performance to make cost of energy delivered from turbines competitive with other forms of energy generation.
Turbine technology has advanced rapidly to provide increasingly reliable turbines and increasingly low cost wind energy. This is partly enabled by a better understanding of the loading environment in which wind turbines operate, which enables better-designed turbines. Turbine blades, the drivetrain, and the overall operation of the turbine have been a particular focus of such cost-reduction efforts.
An exemplar of such a design change to reduce cost is a two-bladed turbine. Two-bladed turbines generally provide lower costs due to a reduction of materials, parts, and weight, which in turn means lower cost of delivered energy. Additionally, two-bladed designs offer other advantages; for example, the turbine system may be assembled on the ground and lifted all at once because of the inherent balance of a two-blade configuration.
Three-bladed designs, however, have gained greater acceptance to date than two-bladed designs. The blades on the turbine may be exposed to considerable imbalance forces, even during normal operation, which causes fatigue in the components of the turbine. Conventional systems compensate by increasing the dimensions of all the main components, which in turn negates the cost benefits of a two-bladed design. In contrast, three symmetrically arranged blades can naturally level out some of the imbalance forces created due to irregularities in the wind or water field.
Several other solutions have been presented to overcome the above design, environmental, and economic issues, and in particular to reduce imbalance forces typical of many turbines, One solution is a teetered hub. A teetered hub design includes two blades rigidly fixed to a teetered hub, which is hingedly connected to the turbine shaft.
An exemplar is U.S. Pat. No. 4,565,929 to Baskin et al. which shows a fixed pitch turbine with a hub able to passively teeter. The teetered hub can rotate through a range of motion in response to varying load forces until making contact with teeter stops. Fatigue behavior is satisfactory during normal conditions, but during extreme wind conditions with high turbulence and wind shear, the hub crashes against the teeter stops. This may result in higher moment forces than a rigid hub wind turbine.
Another solution has been developed to solve the problem of teetered movement in extreme conditions. One example is disclosed in U.S. Pat. No. 5,354,175 to Coleman et al. which discloses a passive teetered hub with an elastomeric saddle bearing, teeter stops, and hydraulic dampeners connected to each turbine blade. During normal conditions, the pre-loaded rubber provides a damping force through the range of teeter motion in accordance with the fixed elastomeric constant of the rubber.
The Coleman device has several limitations. The spring dampeners of the Coleman device apply damping pressure to the rotating blades which leads to significantly increased complexity. Further, mounting dampers to the blades may feed disturbance forces back into the blades, which would negatively affect performance and reliability. The Coleman turbine also calls for a unique dampener system associated with each blade. Each damper must be tuned to work synchronously with the other dampers. Further, the dampeners must act in coordination so as to accurately and efficiently control teeter angle and teeter dampening. The complexity of the system increases the bill of materials and maintenance costs.
Additionally, the Coleman device improves performance only in certain types of conditions. The Coleman dampeners are activated at low RPMs or when the teeter angle exceeds +/−2.5°.
A turbine is advantageously designed to cope with all conditions, whether normal power generation mode or ‘other’ modes including, but not limited to abnormal, extreme, non-operational, and transitions between these conditions. Examples of such conditions include quick, drastic changes in blade loading from gusts of winds, starting or stopping functions, and fault cases. The various wind turbine design and certification standards, such as the IEC standard, define the load cases that are to be considered in designs according to each standard. Such loads include fatigue loads and ultimate loads.
Conventional turbines with dampeners typically include a spring damper having a spring constant that is largely fixed and designed to be most effective during normal operation of the turbine. Such turbines allow for movement or compression of the damper during normal use, but the compression has a fixed spring constant and a certain maximum defined by an end stop or similar limit of deflection. During ‘other’ conditions the damper functions to dampen the approach of the teeter end limits. There is no adaptation or tuning of the system to accommodate and exploit the different dynamics of the system as a whole during operation. Additionally, the end stops may in fact increase load forces during extreme conditions when the spring damper is overcome.
It is advantageous to control teeter motion under “other” operating conditions. For example, during starting or stopping of the turbine, in particular at lower or higher wind speeds, the teeter motion is not operating under the same conditions as at the designed rotational speed of the turbine.
More recently, sophisticated mathematical and computer methods and models have been integrated into turbine designs. Such designs employ the mathematical calculations to reduce loads on the wind turbines and thus increase operational life. An exemplar of such a design is disclosed in U.S. Patent Publication No. 2004/0096329 A1 ('329 publication), now abandoned, the entire content of which is incorporated for all purposes herein by this reference. Such designs use knowledge or estimates of the operating environment to select appropriate components such as a damping member. Various aspects of the '329 publication are directed to selecting a teeter damping value based on an eigenfrequency of the operating turbine.
In spite of the above-described devices, there is a continuing need to increase the performance of turbines and the economics of turbine installation and operation.
What is needed are a turbine and system that overcomes the above and other disadvantages of known systems. What is a needed is a turbine that performs advantageously in myriad, dynamic conditions that may be experienced in real-world applications. What is needed is a turbine with increased reliability and improved efficiency (power yield) in conditions other than average or extreme fluid flow.
What is needed is a system for a turbine that minimizes the effects of imbalance forces caused by irregularities in a fluid field and thus the risk of fatigue and extreme loads in the structure and system. What is a needed is a turbine and system that minimizes the effects of imbalance forces during normal, abnormal, extreme, start/stop, non-operational, and other conditions.
What is needed is a turbine of simple design that improves operational characteristics of the turbine system based on a plurality of the factors related to the system and fluid field. What is needed is a turbine, having one or more blades, for use in a wind field or other fluid field having improved performance, reliability, and robustness.